In addition to dyeing, the lightening of one's own hair color and/or bleaching is a very specific preference of many consumers, because a blond hair color is considered attractive and desirable from a fashion perspective. If substrates are to be lightened or even bleached, the substrate-dyeing dyes, the hair's natural melanin, for example, are typically decolorized oxidatively using appropriate oxidants, such as hydrogen peroxide.
When hair is bleached—more particularly when hair is bleached at home by consumers themselves—the problem is that natural tints become completely covered, making multi-tone hair bleaching difficult to realize.
In order to lend the hair a natural appearance, partially decolorizing both non-dyed and already dyed hair by the targeted application of oxidants is known from the prior art. The hair sections (“strands”) to which the oxidant is applied typically bleach in portions, the result being a multi-tone hair color. Dyeing individual hair sections (“strands”) with a different color is also known from the prior art. The oxidant, possibly including dye, is applied to the hair by employing a brush or similar tool, wherein the hair that is to remain untreated is protected against contact with the oxidant, possibly including dye, by employing solid, flat separating mechanisms or apparatuses, more particularly with soils from solid materials, such as aluminum, paper or Styrofoam and similar materials, or by employing a so-called “highlighting cap”. Such a highlighting cap is disclosed in WO 2007/087978, for instance.
This type of application addresses the problem of the most natural possible coloring of hair, but only enables coloring with “highlights”. For “lowlights”, i.e. darker portions, a subsequent coloring must take place. The cases describe above, therefore, a time-consuming second decolorization or coloration step would be necessary after the first coloring. Therefore, for home use, in particular, the entire hair would have to be colored before the user can add “highlights” or “lowlights”. Many consumers find this to be too time-consuming and frustrating, because the essential color-changing step took place at the beginning and is only “corrected” in a second step.
With the prior art highlighting method, the foils or the highlighting cap accumulate at the end of the method as solid waste, which must be discarded This causes an environmental load. Handling the foils is difficult in part; for example, access to as yet untreated hair is obstructed by foils already in place. Moreover, foils made of paper, plastic and Styrofoam can adhere to the treated hair poorly and slip out.
Certain foil types and applications can involve overheating, because the possibility of dissipating the reaction heat of the exothermic oxidation process by evaporating volatile formula constituents, such as water for example, is severely restricted by the steam-impermeable foils.
Production of commercial hair coloring agents, like the production of other products, is subject to high cost pressure. Therefore, the person skilled in the art strives to harmonize as many recipe components as possible. With coloring creams, for example, a specific emulsion base is used as a “carrier”. Any additives which provide an individualized product benefit—whether dye powder mixtures for a specific nuance or select nourishing agents to treat different hair qualities in an optimal manner—must be as compatible as possible with the carrier, e.g. the coloring cream base. In the process, the so-called color shift is a criterion for compatibility. With the addition of custom additives, color differences can occur between the hair color achieved with the additive-free (standard) carrier and the hair color achieved with the carrier including additive. Such color differences are described by the present application as “color shift”. This color shift, also referred to as dE or ΔE, can be determined by colorimetry by employing a colorimeter, which measures the colors in the L*,a*,b* color space by employing a colorimeter from Datacolor, Type Spectraflash 450, for example.
The L*,a*,b* color space means the CIELAB color space. The L-value denotes the lightness of the color (black-white axis); the higher the value for L, the lighter the color. The a-value denotes the red-green axis of the system; the higher this value, the more the color is shifted into the red. The b-value denotes the yellow-blue axis of the system; the higher this value, the more the color is shifted into the yellow.
The color shift ΔE, i.e. the color difference between two (hair) colors, for which a L*,a*,b* value combination was determined in each case, is calculated according to the following formula:ΔE=(ΔL2+Δa2+Δb2)0.5 
The greater the value for ΔE, the more pronounced the color difference or “color shift”. Color differences with an ΔE<1 are not perceptible to the human eye. Color differences with an ΔE<2 are visible to the trained eye. Color differences with an ΔE>2 are visible even to the untrained eye.
In the worst case, the addition of an additive to a coloring agent carrier causes a color shift, compared to the carrier without additives (standard) with ΔE>2, which is visible to even the consumer's untrained eye. To avoid extensive tests with respect to the achievable hair coloration and, where applicable, the fastness properties having to be carried out with every additive change of the standard carrier, it is therefore desirable to identify active ingredients and nourishing agents for the hair, the addition of which causes no or at least only a minimal color shift.
Patent applications EP2574331A2 and WO2014164213A1 disclose coloring methods that permit multi-tone coloring in one coloring step, wherein a thickening agent, more particularly an anionic or cationic associative polymer (EP2574331A2) having a thickening effect is added to a hair coloring agent in higher concentrations before application to selected hair sections or strands. The coloring agent thickens on the hair strands to form a highly-viscous paste, thereby achieving a separating effect to adjacent hair sections or strands. The color exchange between adjacent strands, which were treated with various coloring or bleaching agents, is thus minimized. Over the total coloring agent application time of approx. 30 to 60 minutes, the dye diffusion between adjacent strands, which are in physical contact with one another, cannot however be completely avoided. The corresponding commercial product for professional salon use is therefore marketed with the instruction that the color difference between adjacent strands should not be more than about 3 color tones. Otherwise, the color result would be impaired by a visible color exchange.